In the manufacture of motor vehicles, there is a need to sense movable parts in order to detect, for example, the distance between the axle body and the vehicle body at any particular time. For this purpose, distance sensors are necessary. The sensor should detect the distance between the two reference points without contact in order that the sensing takes place without being affected.
Distance sensors are also needed for air springs having elastomeric air-spring flexible members for spring supporting components. The distance sensors are here used to control the level of the air springs.
It is known to effect the control of elevation for obtaining an equalized vehicle level for different load conditions utilizing an electronic elevation sensor with the aid of a pair of opposing conical springs in the interior of a flexible member of an air spring. The conical spiral springs are deflected in the axial direction during compression. The springs are electrically connected to each other on one of the connecting plates with which the air spring is connected to a vehicle frame and an axle assembly of the vehicle. The evaluation electronics and the connections for the two other spring ends are on the other plate. A change of the length of the spring effects a corresponding change in the electrical inductance which is converted to a distance signal. An elevation sensor of this kind is, however, very complex The above-described sensor and the air spring are described in the product sheet entitled "ContiTech Luftfedersysteme mit integriertem Hohensensor" published by ContiTech Luftfedersysteme GmbH of Hannover, Germany (1992).